Will switching trial or beta versions, uninstalling, or upgrading erase my work?

No. Scrivener is a standard file-based computer program (rather than a mobile app), which means that it is a separate piece of software on your hard drive that utilises separate files to store your work. While the project format is more complex (technically being a folder of files) it is not at all dissimilar to having .doc files on your computer. If you were to uninstall Word, your .doc files will not be deleted from your computer.

When you created new projects for your work, you were asked where you wished to save them and by what name. If you don't recall doing this, it is likely that they are all stored in your main Documents folder, as this is the program default. While Scrivener has convenience features for tracking the last few projects you've edited, these features should not be relied upon to manage your projects. You should instead familiarise yourself with how projects are stored on your computer, so should you ever have to do a full re-install (and potentially lose the recent projects list), you will have confidence in knowing precisely where everything is.